The present invention relates to a television camera apparatus and, more particularly, to a television camera apparatus having an automatic gain-selecting unit in which the lens-iris value is automatically servo-controlled in response to the level of a video signal picked up through an amplifying means from a pick-up-tube.
In the prior art television camera apparatus, a lens-iris value and the gain of a gain-selecting amplifier inserted in a video signal process (green channel video signal process in a three-tube color television camera apparatus) are controlled as follows: When the intensity of illumination from the object falls or increases, the lens-iris in opened to increase the video signal level or closed to decrease the video signal level. Furthermore, if the lens-iris is fully open and the intensity of illumination falls, an operator manually selects the gain of the gain-selecting amplifier in order to increase the video signal level for maintaining a predetermined signal level. On the other hand, if the lens-iris becomes fully closed and the intensity of illumination increases, he manually selects the gain of the gain-selecting amplifier in order to decrease the video signal level.
Practically, the characteristic of a lens, such as sharpness and contrast characteristics thereof depends on the lines-iris value, and the medium range of the iris value provides a better characteristic. For instance, the better sharpness and contrast characteristics of a lens having a maximum iris value of F.2.8 are delivered at a range of iris values between F.5.6 and F.8.
In the prior art television camera apparatus, the operator has to manually select the gain of the gain-selecting amplifier to maintain the medium range of the lens-iris value and the predetermined video signal level. However, the procedure of the manual controlling operation is difficult for the operator.
It is therefore an object of the present invention to provide a television camera apparatus having an automatic gain-selecting unit which automatically maintains the medium lens-iris value with the predetermined video signal level by selecting the gain of the gain-selecting amplifier, and therefore produces a good S/N ratio-and-contrast video signal.
According to the present invention, there is provided a television camera apparatus comprising a gain-selecting unit which selects the gain of the gain-selecting amplifier in response to the lens-iris value in order to maintain the medium range of the iris value.